The Justice Department has officially ended its inquiry into the assassinations of John F. Kennedy and Martin Luther King Jr., finding "no persuasive evidence" to support conspiracy theories, according to department documents.

A Justice Department memo, obtained by a California ophthalmologist through the Freedom of Information Act, was the department's admittedly long-overdue response to the House Select Committee on Assassinations' recommendation 10 years ago for further investigation.William F. Weld, who was head of the department's criminal division until he quit at the end of March, told Rep. Peter Rodino, D-N.J., chairman of the House Judiciary Committee, that all known leads have been checked.

"The Department of Justice has concluded that no persuasive evidence can be identified to support the theory of a conspiracy in either the assassination of President Kennedy or the assassination of Dr. King," Weld wrote in the undated memo.

"No further investigation appears to be warranted in either matter unless new information which is sufficient to support additional investigative activity becomes available," he added.

The Justice Department's response to the conspiracy theories comes as no surprise. It is, however, the first time the department has made a formal conclusion on the assassinations, said Justice spokesman Dean St. Dennis.

The House Assassinations Committee concluded in 1978 that Kennedy was probably assassinated as the result of a conspiracy involving a second gunman, a finding that broke from the Warren Commission's belief that Lee Harvey Oswald acted alone in Dallas on Nov. 22, 1963. The House panel also said there was a "likelihood" that King's slaying in 1968 was part of a conspiracy.

The committee urged the Justice Department to investigate several areas of the assassinations, and one year later the department agreed to conduct a limited inquiry focusing on an acoustical study presented to the committee by independent experts.

The acoustical experts had concluded after studying a Dictaphone recording of a Dallas policeman's open radio transmissions that there was a second gunman on the infamous grassy knoll who fired a fourth shot. That evidence was the key to the committee's second-gunman conclusion.

Justice officials instructed the National Academy of Sciences to review that study and the Dictaphone recording, and academy scientists concluded in 1982 that the independent experts were wrong.

Weld said the Justice Department had completed "virtually all" of its inquiry by the end of 1983, but delayed its response to the House Judiciary Committee "pending a complete review of all public comment" on the National Academy study.

"We have considered the review of all correspondence to be potentially productive," he said. But he said there was no "persuasive criticism" of the academy report, so the Justice Department has accepted its conclusions.

"All these years later we find out they've been doing nothing," said Kevin Walsh. "Members themselves had faith that the Justice Department was going to pursue this, and now we see all these years later that their faith was misplaced."

Walsh noted that the department did not follow through on several parts of the select committee's recommendations.

The "most egregious sin," according to Walsh, was the department's failure to obtain and analyze a bystander's film shot just minutes before the Kennedy assassination. The film by Charles L. Bronson scans the sixth-floor window of the Texas School Book Depository, where Oswald was positioned.

"If you have film footage that bears on a murder case, you subpoena it," Walsh said. "They didn't even consider it."

Weld wrote that the department was unable to obtain the film from the owner.

The Justice Department conceded that the report to Rodino's committee was "long overdue."

"One of the interesting features of employment with a large governmental organization is that matters occasionally come bubbling to the surface from the depths of the bureaucracy," Acting Assistant Attorney General Thomas M. Boyd wrote in a letter to Rodino accompanying the Weld memo. "An example of this phenomenon is the enclosed report which relates back to the activities of the Select Committee on Assassinations."

Boyd's letter to Rodino was dated March 28 and accompanied the memo from Weld.

The documents were sent to Dr. Louis P. Kartsonis, a San Diego ophthalmologist, on a Freedom of Information Act request he made through Sen. Alan Cranston, D-Calif., and Rep. Bill Lowery, R-Calif.

Kartsonis said he has conducted research and delivered lectures on the Kennedy assassination for more than 15 years. He, too, criticized the Justice Department's inquiry, saying investigators failed to answer the select committee's questions.